This disclosure generally relates to probes and methods for non-destructive evaluation, and more specifically, to eddy current probes and methods for non-destructive inspection of conductive test objects.
Industrial processes often use non-destructive examination to test and/or inspect an object without damaging the object. For example, aircraft components formed of conductive materials often need to be inspected for surface flaws such as cracks. One such method for non-destructive testing of conductive materials for flaws is eddy current inspection. Eddy current inspection is accomplished with probes configured to have current flow in a drive coil line, which results in an electromagnetic field being created. The electromagnetic field induces eddy currents on the metallic test object. The eddy currents so induced in turn generate a secondary magnetic field, which creates a potential difference in sensors (coils or other transducers), whose outputs may be analyzed for flaw detection. If there are no detectable flaws, then the sensors should output uniform voltage. If there are detectable flaws, then the current flow within the test specimen is altered, thereby altering the signals induced in the sensors.
Typical eddy current inspection methods generally assume the orientation of the surface anomaly is known and the probes are designed accordingly. However, in several situations such as, for example, the flat area of an engine disk, cracks can occur in different orientations. From productivity concerns, it is desirable to use array probes to inspect larger surface areas more efficiently. However, current eddy current array probes usually are made up of discrete elements and typically have regions through which small flaws can pass through with low detectability. For example, a prior art eddy current array probe utilizes for each channel, rectangular sense coils offset in the x and y directions with a drive coil encircling each sense coil. However, flaws parallel to the array length that are close to the size of the gap between elements can pass through with low sensitivity. Compensation of the responses from this probe is oftentimes difficult due to the complicated footprints. Another problem is that the high number of drive vias can result in low fabrication yields. Arrays of circular coils have been used by continuously switching the elements in the array to transmit and receive mode. However, the flaw sizes that can be detected using this type of configuration would be larger than the size of one coil. Moreover, there is no consideration as to how to use this probe for flaws that are at angles other than about 0 (i.e., parallel direction to array length) and about 90 degrees (i.e., perpendicular to array length).
Accordingly, it would be desirable to have an improved eddy current probe and methods for robust inspection of flaws regardless of its orientation.